Identification of non-visual photoreceptors in the human eye (so-called intrinsically photosensitive retinal ganglion cells, or “ipRGCs”) linked to the circadian system has sparked considerable interest in the effects of various light spectra on health and amenity for human beings. High circadian stimulation may lead to positive effects such as resetting sleep patterns, boosting mood, increasing alertness and cognitive performance, and alleviating seasonal affective depression. However, mis-timed circadian stimulation can also associated with disruption of the internal biological clock and melatonin suppression, and may be linked to illnesses such as cancer, heart disease, obesity and diabetes.
Circadian stimulation is associated with glucocorticoid elevation and melatonin suppression and is most sensitive to light in the blue wavelength regime. With the preponderance of light-emitting diode (LED) illumination products being based on blue-primary phosphor-converted white-emitting LEDs, the situation has developed that most LED-based illumination sources have higher levels of circadian stimulation than the traditional sources they are intended to replace.
In addition, illumination products are rarely tunable (other than mere dimming), and legacy illumination products fail to address the impact on humans with respect to diurnal or circadian cycles. Still worse, legacy illumination products that are ostensibly tunable fail to produce good color rendering throughout the tunable range.
What is needed is a technique or techniques for constructing illumination products in which light emission (e.g., LED light emission) can be controlled to provide varying levels of circadian stimulation while providing desirable light quality aspects such as correlated color temperature (CCT) and color rendering index (CRI). Also needed is an illumination system in which a first ratio and a second ratio of light emission are such that changing from the first ratio to the second ratio varies relative circadian stimulation while maintaining a CRI above 80 and maintaining the CCT within a prescribed range.
The aforementioned legacy technologies do not have the capabilities to implement a circadian-friendly LED light source in an efficient manner. Therefore, there is a need for improved approaches.